This invention relates generally to absorption cooling systems and to absorption heating and cooling systems and, in particular, to the management of refrigerant for release into the system during part load and shut down conditions.
In an absorption type cooling system, an absorbent is dissolved in a liquid refrigerant to produce a refrigerant-absorbent solution that is suitable for use in the process. When such a system operates under cooling loads that vary, the amount of refrigerant necessary to keep the system running efficiently will also vary. As a result, it is a common practice to equip such a cooling system with a refrigerant adjusting system which includes a refrigerant storage reservoir, and to store refrigerant in or release refrigerant from this reservoir as necessary to keep the concentration of the solution within an acceptable range of concentrations as the cooling load fluctuates. This storage reservoir often takes the form of a sump that is located in or in close association with the system condenser.
One example of a cooling mode refrigerant adjusting system of the above-described type is described in unexamined Japanese application 62-178858, which is assigned to Ebara Ltd. of Tokyo, Japan. In the latter application, there is disclosed an absorption machine in which the gravity flow of liquid refrigerant between the system condenser and the system evaporator is controlled in response to a sensed condition of the system, such as the solution temperature as it is leaving the absorber. A reservoir for liquid refrigerant is provided inside the condenser and the refrigerant is supplied to the evaporator through a first flow path under normal operating conditions. Upon the sensing of a condition that calls for an increase in the quantity of refrigerant, a second flow path is opened which supplies additional refrigerant from the condenser to the evaporator. Another example of a refrigerant adjusting system is described in copending U.S. patent application Ser. No. 09/244,910, filed Feb. 4, 1999, which is commonly assigned herewith, and which is hereby expressly incorporated by reference herein. In this application, there is disclosed an absorption type machine in which refrigerant is stored in a holding tank that is separate from the condenser sump and that is filled via a refrigerant bleed line. The desired refrigerant concentration is then maintained by releasing refrigerant from the holding tank under the control of a microprocessor in response to the sensing of a need for additional refrigerant.
An example of a refrigerant adjusting system that is specially adapted for use in an absorption type refrigerator is described in U.S. Pat. No. 5,806,325 (Furukawa et al). In that patent there is described an absorption type refrigerator in which a storage reservoir is formed in the condenser by a dam with an array of holes that allows the rate at which refrigerant is released to vary as a function of the rate at which refrigerant condenses and, consequently, as a function of the cooling load that the refrigerator must support.
When an absorption type cooling system is shut down, it is necessary to release into the system, within a time known as the dilution time, a quantity of refrigerant which is sufficient to dilute or reduce the concentration of the absorbent-refrigerant solution within the absorber to a value low enough to prevent crystals of the absorbent from forming therein. The diluting of this solution during the shut down process is known as the dilution cycle of the system. Historically, the additional refrigerant necessary to enable the system to complete its dilution cycle has been provided in various ways. One approach was to pump the additional refrigerant from a specially provided storage tank. This approach is not cost effective, however, not only because of the cost of providing such a storage tank, but also because of the cost of providing the associated pump and pump control circuitry.
Another way of providing the additional refrigerant necessary to complete the dilution process has been to release into the system the contents of the refrigerant storage reservoir or tank that is used as a part of its cooling mode refrigerant adjusting system.
This way of diluting the solution, however, has a deficiency that limits its usefulness. This is that the reservoir outlets and piping through which refrigerant is released during the cooling mode refrigerant adjusting process are too small to allow the refrigerant necessary to complete the dilution process to be released within the available dilution time. As a result, the released refrigerant may not be able to mix with the absorbent-refrigerant solution rapidly enough to prevent crystals from forming in the absorber.
While the above-mentioned deficiency may be overcome by providing circuitry which senses the occurrence of a shut down condition, and which opens valves that controllably increase the rate at which refrigerant is released into the evaporator, the provision of such circuitry and valves substantially increases the cost of the shut down portion of the cooling system. The provision of such control circuitry and valves also increases the complexity of the system and thereby introduces failure modes that decrease the overall reliability thereof.
Another approach for providing the refrigerant necessary for dilution has been that shown in U.S. patent application Ser. No. 09/580,182, filed May 26, 2000 which is commonly assigned herewith and which is expressly incorporated herein by reference. There, a refrigerant storage tank is provided in the condenser for storage during the cooling cycle for release along two flow paths during part load and shut down conditions, respectively.
Finally, there is another common approach wherein the refrigerant is stored in the evaporator sump and the level of the refrigerant is sensed so that when it reaches a certain predetermined level, a solenoid valve is opened and refrigerant is dumped to the solution pump either by gravity feed or by using a refrigerant pump. This approach, of course, requires a sensor, a solenoid valve and possibly an additional refrigerant pump.
It is therefore an object of the present invention to provide an improved refrigeration management apparatus for an absorption system.
Another object of the present invention is the provision in an absorption system for a refrigeration management apparatus which stores refrigerant during the cooling process and selectively releases refrigerant to accommodate part load and shutdown conditions.
Yet another object of the present invention is the provision in an absorption system for the storage of refrigerant in a location other than in the condenser.
These objects and other features and advantages become readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.
Briefly, in accordance with one aspect of the invention, a refrigerant storage tank is placed in the evaporator of an absorption system, in fluid communication with both the condenser and an evaporator sump. During cooling mode operation, liquid refrigerant flows from the condenser to the storage tank by way of a conduit, and from the storage tank to the evaporator sump by way of an opening in the side of the storage tank and by way of overflowing the refrigerant tank during full load operating conditions. The size of the opening is such that, under part load conditions, there is sufficient flow of refrigerant to the sump to prevent cavitation of a refrigerant pump associated with the sump. At shutdown, the opening allows for drainage of the refrigerant storage tank into the sump and for the subsequent overflow of the sump into the absorber so as to sufficiently dilute the absorber solution to prevent the formation of crystals.
In accordance with another aspect of the invention, the condenser is fluidly connected to the refrigerant storage tank by way of a J-tube, which provides a liquid seal between the condenser and the evaporator. Also, a liquid/vapor separator may be provided downstream at J-tube such that any vapor that results from a flashing of the refrigerant can be passed to the absorber, with only liquid refrigerant remaining to be passed to the storage tank.
In accordance with another aspect of the invention, the opening in the side of the refrigerant storage tank is a slot which extends vertically to the bottom of the storage tank such that, upon shutdown, the storage tank drains completely to the evaporator sump.
In accordance with another aspect of the invention, the storage tank is replenished by way of a bleed line from the refrigerant pump rather than from the condenser.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.